Variable tuning mechanism



Sept. 21, 1943. F, w GDSEYl JR 2,330,047

VARIABLE TUNING MECHANI SM Filed June 24, 1940 2 SheebS-Sheell 1 FRANK W60055K JR. INVENTOR.

ATTORNEYS.

Sept 1943. F, W. GoDsEY, JR 2,330,047

VARIABLE TUNING MECHANISM Filed June 24, 1940 2 Sheets-Sheet 2 FRANK M!60055K JR. INVENTORL ATTORNEYS.

Patented Sept. 21, 1943 VARIABLE TUNING MECHANISM Frank W. Godsey, Jr.,North Adams, Mass., as-

signor to Sprague Special-ties Co., North Adams, Mass., a corporation ofMassachusetts Application June 24, 1940, Serial No; 342,156'

(Cl. 'i4-10)` 4 Claims.

The present invention relates to an improved method and means foractuating the tuning elements of a radio receiver and more particularlyto novel driving means for actuating a condenser gang comprising tuningcondensers of the type described in the copending application of RobertC. Sprague and Frank W. Godsey, Jr., Serial No. 336,822 filed May 23,1940, now U. S. Patent No. 2,324,178 issued July 13, 1943.

The tuning condenser described in said application comprises condenserunits the electrodes of which consists of two closely-spaced concentricconducting cylinders which are displaceable relative to each other, tovary the capacity of the condenser; Interposed between the electrodes isa -dielectric layer which preferably consists of a vitreous materialforming a fused integral coating on the surface of the inner electrode.Preferably the electrodes andthe coating are made in their coactingdimensions to close tolerances as to engage each other with a smoothlysliding iit.

Tuning condensers of this type have many'advantages, as they combine awide capacity range, great mechanical and electrical stabilitythroughout their capacity rangewith a small size, compact and lightweight structure, and can be manufactured at low cost. l

Such tuning condensers possess inherently a linear capacity-strokecharacteristic, but by means of suitable mechanical driving means the.

relation between the capacity of .the'condenser and the displacementy(or rotation) of the tuning control can be made of any other desiredcharacter.

By observing the various requirements specified.

inthe above referred to copending application of R. C. Sprague et al.,condenser of this type can be made tocapacity tolerances of plus/minus1% and even less. ,In practice however, such condensers .are morefeasibly made to tolerancesl of about plus/minus 5% and consequently theindividual condensers of an assembly may correspondingly differ both intheir capacity range and in their minimum and maximum capacity values.Such wider capacity tolerances as a rule, do not fully meet practicalrequirements. Furthermore, in certain applications, for example, insuperheterodyne `radio receivers, the tuning condenser of the oscillatorcircuit must possess a diierent capacity range from that of the'remaining tuning condensers; to achieve this in the past eitherso-called cut-plate tuning condensers have been used or an eXtra paddercondenser was inserted in series with the tuning condenser of theoscillator circuit. Y

It is an object of this invention to provide novel actuating and drivingmeans `for tuning condensers comprising as their main elements twoconcentric cylindrical electrodes. 'i

Another object of the invention Vis, to provide .ranges and values ofindividual condensers of a gang and thedisplacement (or rotation) of thetuning control means of the gang.

These and further objects of the invention'will appear as thespecification progresses.

The invention will be described with reference tothe appended drawingsforming/part of the specication and in which:

Figure 1 isa side view, partly in section, of a .tuning condenser gangusingA one embodiment .in mass productionto meet theY particular reequirements 4and accurate tuning of its tuning circuits.

Fig. l2' is, aplan view of the condenser gang` of Fig. 1.

Fig. 3 isl a diagrammatic illustration of a method by which theactuating and driving means. ofthe invention permitseach condenser ofthe .assembly to assume an `individual relationship between its capacitysettingV and the displacement (or rotation) of the common tuning controlmeans.A l l Y Fig. 4 is a side view illustrating another embodiment ofthe driving means of the invention as applied-to` a tuningcondenser of aconstruction similar to that of Figs. 1 and 2. i

Fig. 5 is a side View illustrating a modication o-f the driving'meansshown in Fig. 4.

Referringto Figs. 1 and 2, the-tuning condenser gang there showncomprises two condenser vunits supportedV on acommon metal mounting basel5y which in practice is preferably the chassis `of. the; radio receiverin whchthe .condenser gang is used. The two condensers are identical inconstruction and each comprises an electrode I consisting of a hollowmetal cylinder or sleeve preferably closed at one end, and an electrodeII consisting of a hollow metal sleeve surrounding the electrode i0.Interposed between the electrodes IG and II is a concentric dielectriclayer I2 forming an integral-coating on the surface of electrode I0. Thedielectric layer I2 consists preferably of a potassium-lead silicatevitreous enamel as disclosed in the copending application of Stanley O.Dorst, Serial No. 289,292, led August 9, 1939, now U. S. Patent No.2,290,947 issued July 28, 1942. The layer I2 may also consist o othersuitable dielectric materials, for example, of various kinds of vitreousenamels, or may consist of a non-vitreous dielectric material such ascellulose acetate, polystyrene, hard rubber or the like, to whichdielectric materials may Vbe added a ller of titanium dioxide or otherdielectric material to increase the dielectric constant and/or lower thepower factor.

The layer I2 is applied to the electrode I0 preferably by thecataphoretic deposition process described in the copending applicationof Preston Robinson et al., Serial No. 197,692 filed March 23, 1938,which process produces a coating of high uniformity and of eventhickness throughout the length of the coating. As a rule the s odeposited coating is fused and thereafter subjected to surface grindingas described in the above referred to copending application of RobertC.Sprague et al., whereby the coated electrode Ill- I2 engages the sleevevelectrode II with a sliding t whereby the air layer or gap I3 formedbetween the elements is preferably 100025" to .0005 thick.

`electrode I0-I2 and the guide 22 are provided with axial bores throughwhich passes a spindle bolt 2| secured by a nut 31.

Each condenser is supported on the base I5 by a metal mounting bracketI4 secured to the sleeve electrode II through a mounting strip I6 whichis` soldered or otherwise secured to theV outer surface of the sleeveII, and an insulating strip I1 of hard rubber, Bakelite, Isolantite orthe like interposed between the strip I6 and the bracket I4. Thesemembers are secured together respectively by a countersunk screw I8passing through the strip I1 and engaging a suitable tapped hole of thestrip I6 and by a countersunk rivet I9 passing through the strip I1 andthe bracket I4.

The bracket I4 is secured to the base I5 by a screw 20 passing throughthe basel I`5 and threadedly engaging a suitable tapped hole of thebracket I4.

The electrode II is provided for its external electrical connection witha terminal lug 24 consisting of an extending portion of the strip I6whereas the coated electrode Ill-I2 is maintained at ground potential bythe spindle bolt 2I which passes through and contacts an uprightextending portion 38 of the bracket I4. The portion 38 also serves as aguide for the spindle 2| and as astop to limit theV lateral movement inga threaded central bore 3l of the coated electrode III- I2 at themaximum capacity position.

The actuating and driving means for tuning the condensers of theassembly comprises for each condenser the spindle bolt 2I above referredto, two couplers 25 and 30, a connecting rod 2S, and a crank 21 and ahub 28 mounted on a driving shaft 29 which shaft is common to all of thecondenser units.

The coupler 25 consists of a metal block havextending throughout thegreater portion of the length of the coupler and adapted to receive thespindle 2|.

The coupler 39 is a metal block, internally 4threaded throughout itslength and is mechanically connected to the coupler 25 by means of Atherod 26 and pins 32 and 33 passing through the ends of the rod andaflixed to the couplers 25 and 3D respectively.

The crank 21 consists of a metal spindle bolt one end of which issecured within a radial bore of the hub 28 in such a manner as to permitthe free rotation of the spindle while preventing its radial movementrelative to the hub. This is accomplished by a lock screw 35 whichpasses through the hub 28 and engages an annular notch 34 of the spindle21. The extending portion of the spindle 21 is threaded throughout itslength and engages the corresponding threads of the coupler 30.

A set screw 3B secures the hub 28 to the shaft 29. A tuning control (notshown) is affixed to one end of the shaft 29 in well known manner.

The couplers 25 and 30 and the crank 21 form the two adjustment means ofthe actuating and driving means of the invention, by means of which eachcondenser of the tuning condenser gang can assume the tuning range andminimum and maximum capacity values, which meet the particularrequirements of its tuned circuit.

Thus in the embodiment of the invention shown in Figs. 1 and 2 thecapacity range of each condenser unit, limited by the horizontal andvertical positions of the crank 21, is determined by the extent oftravel of the coated electrode Ill-I2 through the sleeve II and this canbe adjusted by varying the eiective length of the crank 21 by itsthreading or unthreading through the coupler 3l).

The upper or lower capacity Values of each condenser is adjusted by itsspindle 2| threading a greater or a lesser length of the correspondingcoupler 25, thus setting the initial position which the coated electrodeIll-I2 assumes with respect to the sleeve electrode II. Whether thespindles 2I of the individual condensers should engage theircorresponding couplers 25 to the same or diiferent extents, and thuswhether the coated electrodes IIl--I2 of the individual condensers arecorrespondingly displaced relative to each other, is determined by thedifferences in the characteristics of the individual condensers and bythe particular requirements of their associated circuits. In generalbecause of the above factors, the degree of engagement is diierent foreach condenser unit and this has been shown in Fig. 2 in which theelectrode Ill-I2 of the lower condenser is shown to be displaced adistance D relative to the corresponding electrode of the uppercondenser.

The actuating and driving mechanism of the invention not only permitsthe individual adjustment of the capacity range and the minimum andmaximum capacity values of each condenser unit of a gang, but also makesit possible to proquirements. ofeach. tuning-circuit and` the;` convldensers canv be made-fto.track as: required for 'vide-a differenti rateof change of capacity with displacement (or rotation) f offtheycommon-.tuning control means. isaachieved by displacing the individualcranks 251 of'V thecondensersa pre- 'determined` angle relative toeachother.' rIihis is-shown in Fig; 3% Whe-rezthe crank, 21? of:- the uppercondenserl is shown to lead? the crank' 211 of theflowerf condenser byan angle- InJFig, 3 the shaft 29 is shown to'be rotated .through anangle a from. its end? or minimum capacity position. By so displacingytliecrank 21" the.. upper Acondensery unit exhibits: throughout itscapacity range a greater rate of change ofi-'capacity than does thelower :condenser unit.

Inlsuch-i'nstances wherefthel cranks 211 are displaced "relative toeachother as above described, one limit of: the'capacity-range may.`occur when the crank' ofthe-lower condenser-is in the horizontalposition' and thel otherl limit may occur when the crankcf thelupperl`condenser isin the .vertical position.

Thus;` by adjusting theA angle.I between the two4 cranks 2, and by;adjusting the upper and lovver-capacitylimitsfandE thefs-troke of eachindivid'ual condenser element, the two condenser units may be madevtotrack each other approximately as required; for4 instance, for thesimultaneous tuning of-iy the oscillator and antenna circuits offsuperhetercdyne radio receiver-s,

In Fig. 4itherevis. show-n a second: embodiment of theactuating anddrivingmeans` of the invention. While in Fig. 4 only-one condenser unitis shown', it shouldbe well`- understood, that the invention isapplicable to a. tuning condenser gang having a plurality off' condenserunits.

Theactuating anddriving means illustrated in Fig. 4 comprises for eachcondenser 4| a spindle bolt 59 similar to the spindle bolt 2| describedin connection with the tuning assembly of Figs. 1 and 2, a coupler 5|,and a cam 52 aflixed to a rotatable shaft 53 common to all of thecondenser units.

The coupler consists of a metal block internally threaded throughout thegreater part of its length and into which the spindle bolt 5D threadedlyengages. At its other end which engages the cam 52, the coupler 5| iseither provided with a roller type cam follower or has a smooth, roundedsurface, as shown at 54.

The cam 52 is a suitable disc preferably metal and its specific detailsand shape are determined by the particular requirements of the circuitin which its associated condenser is used. The stroke of the cam, whichis the difference between the rise of the cam at the start and at theend of its movement, determines the displacement or stroke of the camfollower coupler 5| and hence the capacity range of the condenser,whereas the shape of the cam Within the limits of its stroke determinesthe rate of change of the capacity of the condenser. The capacity valuesof the .condenser at the limits of its capacity range can be varied bythreading or unthreading the spindle bolt 50 in the coupler 5| whichadjusts the initial relative position of the electrodes of the condenser4| as has been fully described in connection with the tuning assembly ofFigs. 1 and 2.

Thus by the use of an individual cam 52 for each condenser of the tuningassembly, and by means of the individual couplers 5|, the capacitl7range, the upper and lower limits of the capacity range and the rate ofchange of capacity of each condenser, are made to meet the particularre- -pression at the endA of the stroke.

the-.simultaneous tuning ofthe oscillator andiantenna. circuits ofIsuperheterodyne receivers.r

To maintain the cam follower coupler 5| in positive contactA with thecam 52 there is providedy about the spindle bolt a compression spring55y one end of which abuts against the couplerv 5|: and? the other end0f which abuts against the'bracket'lll; i

While the use of the compression spring 55 as showninFig. 4, fullymeetstherequirements of maintaining a;v positive Contact betweenf thecam follower 5|l and' the cam 52, such usehas the undesirable featurethat a spring whichis capable ofexerting sufcient pressure in thebeginning of lthe stroke requires a. high force for its com- At the sametimeV the pressure exertedy by the coupler 5| against; the surface ofthe cam 52 increases with the degree of compression ofthe spring 55, andin some cases. they pressure at maximum compression is so great that therotation/ofA the cam 5'2fbyfthe coupler may disturb theisetting of thedriving means. Y

In. Fig. 5 I have shown an improved arrangement inwhich the abovedrawbacks are obviated. The driving mechanism there shown comprisesaspindle bolt- 6|) (shown in part), a cam followercoupler 6|, and a cam62v aiiixed to a rotatable shaft 63, wherebyv positive Contactl betweenthe coupler 6|- and the cam 62' is secured by a tension spring 65. Oneend of the spring is secured to theV coupler 6|, for example, by a pin66'. I have found that'if'the other end of the spring 65isxed directlyto the face of the cam, the required good contact between the coupler 6|and the cam 62 can be maintained without the spring being distorted tothe full extent of the stroke of the cam. If the spring 65 is secured toa point on the face of the cam at or approximating the center of the camsurface, no important change in the length of the' spring takes placethroughout the entire stroke of the cam and a constant pressure isexerted by the coupler 6| on the cam 62 irrespective of the rise of thecam.

This is shown in Fig. 5 in which the spring 65 is secured to the face ofthe cam 62 by a pin 61 at a point corresponding to about the center ofthe cam surface, namely at a point from which substantially equal radiiare formed to all effective portions of the cam surface.

It should be noted that whereas in the foregoing description, theactuating and driving means of the invention has been illustrated in itsuse with tuning condensers in which the inner electrode is movable andthe outer or sleeve electrode is secured to a mounting base, suchdriving means are equally applicable for tuning condensers in which theouter electrode is movable and the inner electrode is arlixed to amounting base.

While I have described my invention by means of specic examples and inspecific embodiments, I do not wish to be limited thereto for obviousmodications will occur to those skilled in the art without departingfrom the spirit and scope of the invention.

What I claim is:

1. In a condenser assembly having a plurality of condenser units eachhaving a movable element, means for actuating the element comprising athreaded member engaging the element, a coupler member engaging thethreaded member and adapted to adjust the element to apre-`detz'erm'ined initial position, and'a crank member having an adjustableeffective length engaging said coupler member and adapted to displacethe element to a predetermined second position, and

means to simultaneously actuate all the elements and displace the sa'mefrom' their said Ainitial position to their said second position, said`means comprising a rotatable shaft common to all of the movableelements and to which the `crank members are affixed.

2. In a condenser assembly having a plurality of condenser units eachhaving a movable element, means for actuating each element comprising athreaded member engaging the element, a coupler member engaging thethreaded `member and adapted to` adjust the element to a predeterminedinitial position, and a crankmem- .ber having an adjustable effectivelength engaging said coupler member and adapted to clisplace saidelement to a predetermined second position, and means to simultaneouslyactuate 'all of the elements anddisplace the same from `displacedrelative to each other about said shaft.

'3. In a condenser assembly having a plurality -of condenser unitseach'having a movable ele.- Iment, means for actuating each elementcomprising a threaded rod member engaging the ele'- ment, a couplermember engaging the rod mem- Hber and adapted to adjust the element to apredetermined initial position, a second coupler member secured to saidfirst coupler member,

asador? and a `spindleV crank member threadedly engaging said secondcoupler member and having an adjustable effective length determined bythe degree of engagement of said second coupler member and the crankmember, said crank member being adapted to adjust the element to apredetermined second position, and means to simultaneously actuate allof the elements and displace the same from their said initial positionto their said second position, said means comprising a rotatable shaftmember common to all of the movable elements and to which the crankmembers of each element are axed.

4. In a condenser assembly having a plurality of condenser units eachhaving a movable element, means for actuating each element comprising athreaded rod member engaging the element, a coupler member engaging therod member and adapted to adjust the element to a predetermined initialposition, a second coupler member secured to said rst coupler member,and a spindle crank member threadedly engaging said second couplermember and having an adjustable effective length determined by thedegree of engagement of said second coupler member and the crank member,said crank member being adapted to adjust the element to a predeterminedsecond position, and means to simultaneously actuate all of the elementsand displace the same from their said initial position to their saidsecond position, said means comprising a rotatable shaft member commonto all of the movable elements and to which the crank members of eachelement are affixed, said crank members being angularly displacedrelative to each other about said shaft.

FRANK W. GODSEY, JR.

